Process for preparing fibrous web



Feb. 17, 1970 L. M. GUENTHER PROCESS FOR PREPARING FIBROUS WEB 2Sheets-Sheet 1 Filed May 5, 1968 a Q m muJJOm Zm mn QuIPOOP INVENTORATTORNEYS Feb. 17, 1970 E T I 3,496,259

PROCESS FOR PREPARING FIBROUS WEB 7 Filed May 3," 1968 I 2 Sheets-Sheetz INVENTOR LLOYD M. GUENTH I? BY I ATTORNEYS United States Patent3,496,259 PROCESS FOR PREPARING FIBROUS WEB Lloyd M. Guenther, Orinda,Calif., assignor to Chevron Research Company, San Francisco, Calif., acorporation of Delaware Filed May 3, 1968, Ser. No. 726,438 Int. Cl.B29c 17/14 US. Cl. 264156 8 Claims ABSTRACT OF THE DISCLOSURE Processfor preparing fibrous web from uniaxially oriented polymer film in whichthe film is fed under tension between the rotating surfaces of a toothedroller having parallel, helical rows of teeth and a presser rollerhaving helical grooves which are complementary to the teeth rows andmate with the teeth rows, rotating the toothed roller and presser rollerin opposite directions substantially synchronously at peripheral speedsabout 1.5 to 20 times greater than the film speed, forcing the teeththrough the film and into the grooves and withdrawing the fibrillatedfilm from between the toothed and presser rollers.

FIELD OF INVENTION This invention concerns a process for preparinghighly regular fibrous webs from uniaxially-oriented polymer films.

INVENTION BACKGROUND Copending application Ser. No. 540,149, filed Mar.31, 1966, and now abandoned, describes a basic method for preparinguniform fibrous webs from uniaxially-oriented polymer films. In generalterms this copending application describes a process wherein the film ispassed between a driven roller covered with card clothing havingregularly spaced points and a rotating, resilient presser or backingroller. The direction in which the film travels is substantiallyparallel to the rollers and perpendicular to a plane joining thelongitudinal axles of the two rollers. These rollers are rotating suchthat the portions of their peripheries which are contacting the film aremoving 1n the same direction as the film. The presser roller exertssuflicient pressure on the film to cause the clothing points to punctureand penetrate the film. The driven roller is run such that itsperipheral speed is about 1.5 to 20 times the film speed. Thus, theclothing points act as cutting elements and cut through the film to givea uniformly fibrillated material.

Although the above-described process has been used commercially toprepare uniform fibrous products for use in the textile industry, oneimportant operating difficulty has been experienced. This difiiculty isthat the card clothing has to be replaced frequently because of wear.This, of course, causes considerable loss of operating time. Also, asthe card clothing wears the fibrous web becomes less uniform. Thisincreasing irregularity is refiected in the quality of the end textileproduct.

INVENTION DESCRIPTION A novel improvement in the above-described generalprocess has now been discovered which decreases significantly the wearon the cutting elements of the driven roller. At the same time, thisunique improvement gives a fibrous web of much higher uniformity thanthe previously used process.

The improvement of this invention involves several important changes inthe above-described process. In the improved process of this inventionthe film, while under controlled tension, is fed between the rotatingsurfaces of a driven toothed roller having parallel helical rows of3,496,259 Patented Feb. 17, 1970 sawtooth-shaped teeth and a drivenpresser roller having helical grooves. The rows of these teethcommunicate with the presser roller grooves. The grooves are wider thanthe teeth widths and deeper than the teeth heights. The film is fedbetween the two rollers at an angle such that it contacts the presserroller surface before it contacts the toothed roller and is supported onthe surface of the presser roller. The presser and toothed rollers aredriven synchronously at peripheral speeds about "1.5 to about 20 times,preferably 2 to 15 times, greater than the film speed. The rows of teethpuncture the film and enter the grooves. Because the rollers aretraveling faster than the film the teeth out elongated slits through thefilm. Because the teeth and grooves are traveling substantiallysynchronously, the teeth remain in the groove while they are slittingthe film. The position of a tooth in a groove is such that the distancebetween the groove edge supporting the unslit film and the nearest edgeof the tip of the tooth is less than the lateral off-set distancebetween points of adjacent teeth in a row. The film is withdrawn frombetween the rollers at an angle such that it remains supported on and incontact with the presser roller surface after the teeth have finishedslitting and disengage the film.

The general technology for preparing the film used in this process iswell known in the art. The polymer is extruded in a conventionalextruder to provide a film of desired thickness and width. Forconvenience, a very wide film may be extruded and then slit and trimmedto the desired width. The film may be oriented by drawing it at elevatedtemperatures. Draw temperatures will depend on the polymer used. Thefilm may be heated to the desired temperature by passing it through aheating zone or over heated rolls or drums. It may be drawn in a singlestep or in a plurality of steps. The particular draw ratios used toorient the film will be ultimately at least about 4:1 and may extend toa ratio below that which causes the film to fibrillate spontaneously.The ultimate draw ratio in a given instance will again depend on thepolymer used. For instance, draw ratios between 6:1 to 10:1, preferably7:1 to 9:1, are desirable for normally solid, substantially crystallinepolypropylene.

The film thickness should be chosen to correspond to the finenessdesired in the fibrous product. The thickness of the oriented film usedin the process here described is substantially uniform. Generally, theoriented film thickness will be between about 0.5 and about 3 mils,preferably 0.7 to 2 mils. Lower thicknesses within this range are usedto make fine products with good band. Thicknesses in the upper portionof this range give coarser materials.

The polymers which may be used to prepare these films are orientable,normally solid, crystalline polymers and copolymers. Typical examples ofsuch polymers are high density polyethylene, polypropylene, poly 4methyl 1- pentene, polyester-s, polyamides, e.g., the nylons, and thelike. Mixtures of such polymers may be used if desired. These polymersmay also contain additives such as photo stabilizers, antioxidants, heatstabilizers, dye acceptors, pigments, dyes, fillers and the like.

The driven toothed roller which is used in this invention may be madeconveniently by forming grooves in the circumferential surface of aroller of desired diameter, usually about 2 to 15 in., in helicalparallel rows at angles of about /2 to 45 and setting the blade portionof a sawtooth garnett wire into the groovesleaving the garnett wiresteeth exposed and extending radially from the rollers circumferentialsurface. Desirably, the rows of wire around the roller are equallyspaced. Similar garnett Wire wrapped rollers are used in the textile arefor shredding natural staple fibers.

The working angles of the teeth of the garnett wire used in thisinvention are desirably about 90". If the working angle is significantlyacute the fibrous web is more likely to catch on the teeth and bewrapped around the toothed roller. The lateral offset distances betweenthe points of adjacent teeth are substantially the same and are about Ito about 50 mils, preferably to 15 mils. Since each tooth acts as acutting element, this distance approximates the fibril width in the web.In other words, an individual fibril is formed by the cutting action oftwo adjacent teeth in a row which are ofiset from one another in alateral direction because of the helical wrap of the wire. The teeth areusually tapered in cross section and their tips are usually fiat andabout 1 to about mils wide. The teeth bases are normally about to about25 mils wide. Normally, there are about 3 to 15 teeth per inch of wire.

In order for each tooth of the garnett wire to cut substantially equallength slits in the film, the tolerance in the distances from thetoothed roller axle to the tips of the teeth should be small. Desirably,the varition in these distances should not be greater than about 2 mils.

Practically any number of teeth rows greater than 1 may be used in thisinvention. In any given instance the preferred number of rows will varydepending on the web pattern desired, the toothed rollers diameter andperipheral speed and the penetration. Penetration may be viewed as thatportion of the tooth height which pierces the film. Generally the numberof rows will be within the range of 4 to 30.

The circumferential surface of the presser roller as contemplated hereinis helically grooved such that selected grooves mate with selectedrespective rows of teeth on the toothed roller. That is, the grooveshave substantially the same slope as the teeth rows and the longitudinal(parallel to the roller axis) distance between adjacent grooves issubstantially the same as the longitudinal distance between adjacentrows of teeth. However, the slope of the grooves is negative relative tothe slope of the rows of teeth. As previously indicated, the groovewidth is greater than the tooth width. However, excessively wide groovesshould be avoided since the film may fold into such grooves, resultingin uncut portions in the film (referred to as skipping). Usually thegrooves are about to 60 mils wide.

The grooved presser roller is subjected to substantial friction becauseit contacts the film and moves faster than the film. Therefore, thisroller will desirably be made from hard materials such as chromeorceramic-coated steel. Other materials such as hard plastics, e.g., nylonor Teflon, may also be used. The toothed roller may also be made of theabove-described materials. The presser roller will also normally beabout 2 to about 15 inches in diameter.

This invention may be further understood by referring to the drawings inwhich:

FIGURE 1 is a schematic diagram of the film-forming and filmfibrillating apapratus used in this invention;

FIGURE 2 is a partial side view of the fibrillating rollers of FIGURE 1;

FIGURE 3 is a partial cross-sectional view of the fibrillation apparatusin FIGURE 1 showing a tooth set within a presser roller groove;

FIGURE 4 is a detailed partial view of the fibrillation apparatus ofFIGURE 1; and

FIGURE 5 is a photograph of the fibrous web prepared using thefibrillation apparatus of FIGURE 1.

FIGURE 1 illustrates extruding means 1 for forming film 13 andorientation means 3 for uniaxially orientting film 13, nip rolls and 26,toothed roller 11, presser roller 12, a motor for driving synchronouslythe toothed roller and presser roller (the belt drive system couplingthe toothed roller and driven roller is not shown), pull rolls 27 and28, a motor for driving the pull rolls, take up roll 7 and a motor fordriving the take up roll.

The relative position of the rollers, teeth and grooves are illustratedby FIGURES 2 and 3.

FIGURE 2 represents a view of toothed roller 11 and presser roller 12taken in the opposite direction from which film 13 is traveling. Toothedroller 11 and presser roller 12 are positioned with their respectivecircumferential surfaces parallel and closely adjacent to and spacedapart from each other. The toothed roller 11 retates clockwise and thepresser roller 12 rotates counterclockwise so that the surfaces of eachroller in contact with film 13 travel in the same direction as film 13.As the rows of garnett wire teeth 14 puncture film 13 the teeth meshinto complementary presser roller grooves 15. The lateral offsetdistance between adjacent teeth in a row is a. The helix angle, 6, ofthe grooves is substantially the same as the helix angle of the teethrows but negative relative thereto.

FIGURE 3 represents a partial cross section of tooth 14 within groove15. While the groove is shown as being rectangular, it need not be ofthat configuration. For instance, it may be trapezoidal or have arounded bottom. The groove height is b. As indicated previously, thegroove width, c, will depend on the tooth width and the desired fibrilwidth. In general, the tooth does not have to sit symmetrically in thegroove. It may be closer to the edge of the groove which supports theunslit film. In FIGURE 3 this edge is represented as 16. The gap betweenedge 16 and the tip of the tooth is represented as d. It is this gapwhich is preferably less than the desired fibril width. Thus, as ageneral rule, as the desired fibril width decreases, the distance a mayalso be decreased. As an example of the relationship between the sizesof the teeth, groove and fibril, tapered teeth 9 mils wide at the tipand having a 14 mil lateral offset distance were used with 30 mil widepresser roller grooves. The teeth sat approximately in the center of thegrooves and the gap between the groove edge supporting the unslit filmand the teeth was about 8 to 12 mils. With these dimensions a uniformfibrous web with 14 mil wide fibrils was made.

In the previously used process, the film was passed in a straight linebetween the driven roller and presser roller. However, with the newtoothed driven roller and grooved presser roller if the film is passedin the same manner, i.e., tangentially, between the rollers the fibrousweb had both a fuzzy appearance caused by loose broken ends andirregularities due to skipping. Unexpectedly, it was found that thesedifliculties could be overcome by (a) keeping the film under controlledtension and (b) maintaining it in contact with and supported on thesurface of the presser roller by feeding and withdrawing it from betweenthe rollers at certain angles. Accordingly, in this improved process,the film is fed to and withdrawn from the rollers such that the portionof the film being processed contacts the presser roller before itengages the teeth and remains against the presser roller until the teethdisengage that particular portion of the film. The fibrous web producedin this manner no longer has the fuzzy appearance of the prior art web.This feature of the process may be more readily understood by referringto FIG- URE 4.

FIGURE 4 represents a partial side-view of the film 13 passing betweentoothed roller 11 and grooved presser roller 12 according to thisinvention. Film 13 is fed between toothed roller 11 and presser roller12 at angle a. As illustrated, angle (l is the angle defined by atangent drawn at the point where the film initially contacts groovedpresser roller 12 and a chord intersecting the arcs of toothed roller 11(measured to the teeth tips) and grooved presser roller 12. In orderthat the film contact presser roller 12 first, this angle in radians isgreater than 2 PDI where p is the depth of the greatest penetration ofthe teeth into the grooved presser roller, D is the toothed rollerdiameter measured to the tip of the teeth and D is the presser rollerdiameter. This angle will usually be about 3 to 15. Accordingly, thefilm contacts the presser roller first and then is engaged by the teeth.As the teeth 14 puncture the film they move up into presser rollergroove 15. They cut substantially equal length slits through the filmbecause of the difference in the toothed roller speed and the filmspeed. The film remains in contact with the presser roller after theteeth disengage the portion of the film exiting from between therollers. The fibrillated film is withdrawn from between the rollers atangle 5. As illustrated, angle 5 is the angle defined by a tangent drawnat the point on the presser roller where the film disengages the presserroller and the chord intersecting the arcs of the presser and toothedrollers. The minimum for angle B is the same as that described above forangle a. For convenience angle a will usually be substantially the samemagnitude as angle 5.

The controlled tension applied to the film while it is in contact withthe presser roller is of a magnitude sufficient to keep it held tightlyagainst the presser roller without pulling it into the presser rollergrooves. Normally this tension will be about 600 to about 3000 p.s.i. Iftensions below about 600 p.s.i. are used the fibrous web may have looseends and irregularities caused by skipping. Tensions greater than 3000psi. may be used but they cause increased presser roller wear andrequire greater power inputs. This tension may be effected by passingthe film between nip rolls 25 and 26 of FIGURE 4 before it entersbetween the toothed and presser rollers and between pull rolls 27 and 28of FIGURE 4 downstream of the rollers. The nip rolls ahead of theslitting operation anchor the film against the pull of the teeth. Thetension may be adjusted within the above-mentioned range by increasingthe speed of the pull rolls to a value about A% to about 1% greater thanthe speed of the upstream nip rolls.

EXAMPLES The following examples illustrate the process and apparatus ofthis invention. These examples are not intended to limit the inventiondescribed herein.

Example 1 Commercial substantially crystalline polypropylene wasextruded as a continuous film at a rate of about 30 feet per minute. Thefilm was trimmed to a width of inches and then oriented by stretching itover heated rollers at 250280 F. The ultimate draw ratio was about 7:1.In this way there was produced a film about 7 /2 inches wide and 1 milthick. A thin coating of an aqueous emulsion of an antistatic agent wasapplied to the bottom of the film.

This oriented film was fed through a set of nip rolls and then between atoothed roller and a presser roller. The set of nip rolls was running ata peripheral speed of 200 feet per minute. Both the toothed roller andpresser roller were rotating at a peripheral speed of 709 feet perminute but in opposite directions. These two rollers were coupled by atiming belt drive system and thence to a common drive shaft. The toothedroller was helically wrapped with garnett wire and the other drivenpresser roller was helically grooved in such a way that the garnett wireteeth meshed with and penetrated into the grooves.

The garnett wire wrapped roller was inches long and 6.92 inches indiameter as measured to the tip of the teeth. This roller was covered by16 separate, essentially parallel rows of garnett wire teeth wrappedhelically in a right hand thread. Rows of teeth were equally spaced at11 per inch. Each row contained 3.9 teeth per inch along the garnettwire. The leading edges of the teeth were perpendicular to the rollerface, i.e., they had a 90-degree working angle. Each tooth was 0.009inch thick at the tip.

The grooved presser roll was 15 inches long and 6.92

inches in diameter. Sixteen helical grooves 0.020 inch wide, about 0.05inch deep and equally spaced at 11 per inch were cut into the face ofthe roll. The grooves were cut with a left hand thread. The surface ofthis roller was about 0.06 inch from the surface (at the base of theteeth) of the toothed roller which resulted in a maximum depth ofpenetration of a tooth into a groove of about 0.015 inch.

The oriented film contacted the grooved presser roller at an angle of 7from tangential and it also left the grooved roll at an angle of 7. Thefibrillated film then passed through a pair of pull rollers. These pullrollers were turning at a peripheral speed of 201 feet per minute.

A sample of the fibrous web produced in accordance with the above wasspread to about three times its original width, photographed, and thephotograph enlarged about 2.5-fold. This photograph constitutes FIGURE5. The number of fibrils per inch of width of web averaged 55 for thisweb.

As illustrated by FIGURE 5, the fibrous web produced by this processconsists of bands or ribs 30 connected by rows of longitudinal fibrils31 having a herringbone pattern. The ribs slope laterally across the web(film) width. The angle at which the ribs slope is in the same generaldirection as the slope of the teeth row but greater in magnitude. Thefibrils which connect these ribs are of uniform width and length. Theinterfibrillar spaces are substantially the some. The uniformity of theweb may be estimated b drawing perpendicular lines across the web widthat random intervals and counting the number of fibrils intersecting eachline. The variation in the counts is an indication of the uniformity. Inthe old process, such measurements indicated relative standarddeviations as great as about 20%. In this improved process the relativestandard deviation rarely exceed 3 EXAMPLE 2 A semiworks production ofhighly uniform fibrous web was made using the general process describedin Example 1, but with longer toothed and presser rollers and acorrespondingly wider film. Fibril counts were taken on the fibrousproduct at various times throughout a several weeks run. Thesemeasurements showed that the material had 71 /2 fibrils per inch ofwidth with a standard deviation of 2. Each fibril was 0.035 inch longand each rib was about 0.014 inch wide.

A solid-colored product from this semiworks run was slit into narrowstrips, twisted at two turns per inch and woven into a carpet. Thiscarpet had a completely uniform appearance throughout its length andwidth, without any streaks due to nonuniformity. Carpets produced fromfibrillated material having the same average number of fibrils per inchof width but with a relative standard deviation of about 20% had clearlyvisible streaks and were unacceptable for commercial sale.

As will be evident to those skilled in the art, various modifications onthis invention can be made or followed, in the light of the foregoingdisclosure and discussion, without departing from the spirit or scope ofthe invention.

I claim:

1. Process for preparing a highly uniform fibrous web from a uniaxiallyoriented polymer film comprising feeding the film while under tension inthe range of about 600 to about 3000 p.s.i. between the rotatingsurfaces of a toothed roller having parallel helical rows ofsubstantially equidistant teeth, the working edges of the teeth beingthe leading edges, and a presser roller having helical groovescommunicable with said rows, said film being fed at an angle such thatthe film contacts the presser roller surface before it contacts thetoothed roller and is supported on the surface of the presser roller,said toothed and presser rollers rotating substantially synchronously atperipheral speeds about 1.5 to about 20 times greater than the filmspeed, forcin said teeth through said film and into said grooves so asto cut elongated slits through said film, the distance between the edgeof the groove which supports the unslit film and the tips of the teethbeing less than the lateral off-set distance between the points ofadjacent teeth in a row and Withdrawing the film from between saidsurfaces at an angle such that the film remains supported on and incontact with the presser roller surface until the teeth disengage thefilm.

2. The process of claim 1 wherein the polymer is normally solid,substantially crystalline polypropylene and the film is oriented to adraw ratio between 6:1 and 10:1 and about 0.5 to about 3 mils thick.

3. The process of claim 1 wherein the peripheral speeds of the presserand toothed rollers are about 2 to times greater than the film speed.

4. The process of claim 1 wherein the helix angle of the rows of teethis about /2 to about and the lateral off-set distance between the pointsof adjacent teeth in a row is about 1 to about mils.

5. The process of claim 1 wherein the helix angle of the rows of teethis about 5 to about 15 and the lateral off-set distance between thepoints of adjacent teeth in a. row is about 5 to 15 mils.

6. The process of claim 1 wherein the working angles of the teeth areabout 7. The process of claim 1 wherein the diameters of the toothed andpresser rollers are about 2 to 15 inches,

the angles at which the film is fed between and withdrawn from thesurfaces are individually greater than References Cited UNITED STATESPATENTS radians 2,853,741 9/1958 Costa. 3,137,893 6/1964 Gelpke 264-156XR 3,273,771 9/ 1966 Beaumont. 3,302,501 2/1967 Greene. 3,369,435 2/1968Boultinghouse.

FOREIGN PATENTS 1,010,206 11/1965 Great Britain.

ROBERT F. WHITE, Primary Examiner R. R. KUCIA, Assistant Examiner US.Cl. X.R.

